Github issue: #6621
The problem: for some reason the https://github.com/bradyt/dart-mode repo was deleted, so users of Doom’s :lang dart module will see errors when installing/updating it.
What’s being done: This was reported to MELPA, so I expect it to be resolved soon, otherwise I’ll update the recipe to use a mirror.
The workaround: in the meantime, you can fix this locally by overriding Doom’s recipe to use this mirror:
;; in $DOOMDIR/packages.el
(package! dart-mode :recipe (:repo "emacsfodder/dart-mode"))
Then run $ doom sync -u
and restart Emacs.